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First post on this forum! My girlfriend has a 77 GS550 that has never ran well since she got it. 31,000 miles and left outside for a long time, was pretty rusty and nothing worked right when she got it.
We've done a lot of work to it replacing small parts and getting all the gremlins out, but hadn't gotten the engine to run well yet. After she replaced the cables and some small work, and did a lot of carb work with one of her friends, it still wasn't running well. We upgraded the points to Dyna electronic ignition. Now, with a much hotter spark with the electronic and new wires and coils, all of the sudden we were getting a backfire all the time out of the right side. Set timing by ear at first. It bogged down big time when you would give it gas.
Today, we were tinkering with it for a long time, fixing some oil leaks, installing kick starter, etc. I got the timing light out to tune it, and got it set as best as I could , but the marks were jumping around under the gun. 1 and 4 fire simultaneously, and I thought it was cool that there were also timing marks 180 out for 2-3 (new to motorcycle mechanics), so I put my timing light on the other cylinders as well. THEN, I noticed 4 was not firing all the time! pulled the plug out, pretty black. cleaned, put back in, no change. Plug wire was arcing if I'd hold it close to the chassis, pretty much all the time non stop. The spark on the timing light would drop out a randomly, sometimes for 5 or 7 seconds at various rpm's. After replacing the plug with a brand new one, still, poor running conditions.
So I started doing a compression test, fearing bad valves or rings. Not sure if I was doing it right, maybe cranking too much for a motorcycle engine (tinker with old cars a lot primarily), but I thought that #4 was only at 70-90psi. I forgot and had #2 still hooked up and it started firing. Well, I did #1 and got 120 dry for reference. then I dumped a cap of oil from the quart jug into the cylinder. This got the offending cylinder up to 120 in two cranks. Thought the rings were bad. Ran it for a bit, burnt off the oil so I thought, working in the dark and late for dinner, rushing through things. Then I put more oil than necessary in, two caps from the oil jug, tested, 155psi.
Out of time, had to throw it back together in case she rode it tomorrow. Tried to run it and burn off the oil again, blowing smoke out the right bank exhaust. She test rode it around the block and said it has never ran that good ever! I was thinking that the oil just needed to burn off and it would go back to misfiring all the time and backfiring in #4.
After our company left, we both took it out, thinking that we just had some oil between the rings, sealing things temporarily. We rode it for a half an hour to 40 minutes, up to about 6000 rpm, a lot of highway, and it still rode great. Ever since the beginning of this test ride, no smoke really out the right side. I was thinking that was peculiar for just having dumped two caps of oil into the cylinder. Told her to ride the hell out of it tomorrow to see if it got worse.
So I am wondering if I either did the compression test wrong or something (o-rings smashed down, cranking too much or fast, etc will retry if it starts running bad again), or if I just temporarily got a lot of oil in between the rings to temporarily seal it, or if somehow by some weird chance, taking the spark plugs in and out several times had given me a better ground on #4 (that would be very strange), and that was all that was wrong? Plugs were from previous owner a year and a half or more ago, all else in the ignition is brand new. It's running excellent after that ride, but not sure how long it will last. Not sure whether it was the wet compression test sealing it up for a short while, or if somehow there was a weird grounding problem with the spark plug and threads? That would be really strange if so.
Any opinions or suggestions?
ALSO, MORE IMPORTANTLY, We have an opportunity to buy an 81 GS550 engine with real low miles that runs great for $400. I was thinking that if it needed totally rebuilt, that this engine would be an excellent deal if it would bolt up. Everything external to the engine looks identical pretty much, both are just 8 valve engines. powerband specs were the same for all GS550's except the Katana engines I think it was. I know the carbs were exclusive to 77-78 or 77-79, b ut it looks like they may bolt up to the 81 engine also, but we have not verified. This 81 engine is like brand new. Are there any issues with this swap? I think 80+ had electronic ignition already, so we can use the same coils and wires, etc.
If the engine goes south again, we will probably opt to swap the whole thing out if this is possible, to avoid a lot of machine shop fees, parts, and paying someone with more time and experience to rebuild the engine for us.
Help us out if you can!
Thanks,
Chuck and Reda
We've done a lot of work to it replacing small parts and getting all the gremlins out, but hadn't gotten the engine to run well yet. After she replaced the cables and some small work, and did a lot of carb work with one of her friends, it still wasn't running well. We upgraded the points to Dyna electronic ignition. Now, with a much hotter spark with the electronic and new wires and coils, all of the sudden we were getting a backfire all the time out of the right side. Set timing by ear at first. It bogged down big time when you would give it gas.
Today, we were tinkering with it for a long time, fixing some oil leaks, installing kick starter, etc. I got the timing light out to tune it, and got it set as best as I could , but the marks were jumping around under the gun. 1 and 4 fire simultaneously, and I thought it was cool that there were also timing marks 180 out for 2-3 (new to motorcycle mechanics), so I put my timing light on the other cylinders as well. THEN, I noticed 4 was not firing all the time! pulled the plug out, pretty black. cleaned, put back in, no change. Plug wire was arcing if I'd hold it close to the chassis, pretty much all the time non stop. The spark on the timing light would drop out a randomly, sometimes for 5 or 7 seconds at various rpm's. After replacing the plug with a brand new one, still, poor running conditions.
So I started doing a compression test, fearing bad valves or rings. Not sure if I was doing it right, maybe cranking too much for a motorcycle engine (tinker with old cars a lot primarily), but I thought that #4 was only at 70-90psi. I forgot and had #2 still hooked up and it started firing. Well, I did #1 and got 120 dry for reference. then I dumped a cap of oil from the quart jug into the cylinder. This got the offending cylinder up to 120 in two cranks. Thought the rings were bad. Ran it for a bit, burnt off the oil so I thought, working in the dark and late for dinner, rushing through things. Then I put more oil than necessary in, two caps from the oil jug, tested, 155psi.
Out of time, had to throw it back together in case she rode it tomorrow. Tried to run it and burn off the oil again, blowing smoke out the right bank exhaust. She test rode it around the block and said it has never ran that good ever! I was thinking that the oil just needed to burn off and it would go back to misfiring all the time and backfiring in #4.
After our company left, we both took it out, thinking that we just had some oil between the rings, sealing things temporarily. We rode it for a half an hour to 40 minutes, up to about 6000 rpm, a lot of highway, and it still rode great. Ever since the beginning of this test ride, no smoke really out the right side. I was thinking that was peculiar for just having dumped two caps of oil into the cylinder. Told her to ride the hell out of it tomorrow to see if it got worse.
So I am wondering if I either did the compression test wrong or something (o-rings smashed down, cranking too much or fast, etc will retry if it starts running bad again), or if I just temporarily got a lot of oil in between the rings to temporarily seal it, or if somehow by some weird chance, taking the spark plugs in and out several times had given me a better ground on #4 (that would be very strange), and that was all that was wrong? Plugs were from previous owner a year and a half or more ago, all else in the ignition is brand new. It's running excellent after that ride, but not sure how long it will last. Not sure whether it was the wet compression test sealing it up for a short while, or if somehow there was a weird grounding problem with the spark plug and threads? That would be really strange if so.
Any opinions or suggestions?
ALSO, MORE IMPORTANTLY, We have an opportunity to buy an 81 GS550 engine with real low miles that runs great for $400. I was thinking that if it needed totally rebuilt, that this engine would be an excellent deal if it would bolt up. Everything external to the engine looks identical pretty much, both are just 8 valve engines. powerband specs were the same for all GS550's except the Katana engines I think it was. I know the carbs were exclusive to 77-78 or 77-79, b ut it looks like they may bolt up to the 81 engine also, but we have not verified. This 81 engine is like brand new. Are there any issues with this swap? I think 80+ had electronic ignition already, so we can use the same coils and wires, etc.
If the engine goes south again, we will probably opt to swap the whole thing out if this is possible, to avoid a lot of machine shop fees, parts, and paying someone with more time and experience to rebuild the engine for us.
Help us out if you can!
Thanks,
Chuck and Reda
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